350 ISC Vibration

[4cole_man2]

I just purchased a 2001 Monaco Windsor with a 350 ISC motor. Any time engine rpm exceeds 1750-1800 rpm I get a vibration that can be heard more than felt throughout the entire coach. Definitely engine rpm related and not drive train related, as the frequency does not change with vehicle speed, it is the same whether in first gear or fifth gear. Engine load doesnt seem to be a factor either, the vibration is the same if it down shifts on a steep grade or if I just hold it in gear on flat ground.
Other than the vibration issue it seems to run just fine. All of the filters, air, both fuel, coolant and oil, were changed right after I bought the coach about 3 weeks ago. The gauge readings are all normal.
Obviously the next step is to take it to a Cummins shop and let them try to diagnose the problem, but I thought I would try here first.

[ua40j]

There are a lot of things hanging on this engine. Check your belts and pulleys on the A/C, air compressor and hydraulic (power steering) pump. Check the slop in the main belt and also see if the belt tensioner is doing it's job.

Other obvious things are best checked when on the dyno at Cummins. You can get the engine up to the vibrating rpm on the dyno and then have a good look around.

Good luck finding the cause and let's hope it's inexpensive to fix.

[kenenders]

Check u joints for wear.

[HeapBigEngin]

We have an ISC in our F/Wood Revolution....side radiator. If the hydraulic fan pump is "going away" so to speak, they can develop an RPM-related vibration. A leak at the fan hub is a telltale sign....and not good. Or if the fan itself has been significantly knicked or chipped or has any type of stuff sticking to it, it will definitely set up an incredible vibration. (Please don't ask how I know this!) Normally, however, one would expect to feel it as well as hear it.

Like ua40j stated, there are a lot of thing hanging back there. You might raise the engine cover and have someone rev the engine in neutral at the suspect RPM and see it you can hear, see or feel something back there. If you're lucky, it might just be an old worn or cracked a/c or serpentine belt that's setting up a vibration and needs replacing. As you know, diesel's can be a bit prone to vibration, hence the industrial strength nature of brackets, bolts, hardware and such. Maybe something has loosened up a bit back there. Also, do you have records indicating that anything back there had been changed or replaced prior to your ownership. Just a thought....

PLEASE let us know what you find out....thanks!

[sdelerio]

check the vibration damper on the end of the crankshaft

[David K]

I would check the drive shaft U joints ---- I had a problem with the u-joints on mine and it sounded like what you are describing. Ride height was my problem (not set correctly) and it caused the u-joints to fail.